Due to request for low abrasion on rotational elements to achieve an extended life and for low extent of noise, hydrodynamic bearings have been used in conventional motors such as fan motors or HDD motors.
A typical hydrodynamic bearing comprises a bearing surface to define a bearing hole, and a shaft rotatably received in the bearing hole with a bearing clearance formed between the bearing surface of the bearing and an outer surface of the shaft. Lubricating oil is filled in the bearing clearance. Hydrodynamic pressure generating grooves are provided in either the bearing surface of the bearing or the outer surface of the shaft. Upon rotating of the shaft, the lubricant is driven with the rotating shaft due to the viscosity of the lubricant. A lubricating film is thus formed in the bearing clearance by means of hydrodynamic action of the hydrodynamic pressure generating grooves, so as to support the shaft without radial contact between the shaft and the bearing.
In designing the hydrodynamic bearing, the following factors must be considered. Firstly, appropriate sealing is required at ends of the bearing. This is because, on one hand, the lubricating oil must not leakage from ends of the bearing, or a lubricating oil shortage may occur, which results in a failure of generation of the hydrodynamic press; On the other hand, the lubricating oil must not be polluted by outside dusts entering the bearing, because the dusts will affect the viscosity of the lubricant, which probably also leads to a failure of generation of the hydrodynamic press. Secondly, during motor operation, especially in a fan motor, the rotor rotating at high speed tends to float over the bearing. Such float will cause the rotor to come off the bearing. Therefore, measures must be taken to control the extent of such float to prevent the rotor from coming off the bearing.
For the foregoing reasons, there is a need for a hydrodynamic bearing assembly which can prevent lubricant leakage, lubricant pollution and rotor's coming off the bearing.